The invention relates to an arrangement suitable for amplifying a modulated carrier signal the amplitude variations of which are smaller than the amplitude of the unmodulated carrier.
In recent years numerous modulation methods aimed at achieving efficient data transmission over telephone lines have been designed and introduced. In almost all cases these modulation methods have resulted in a modulated carrier signal having amplitude variations (i.e. amplitude modulation), using linear modulators and amplifiers.
However, these modulation methods are not so suitable for data transmission over radio links because, in radio communication systems, the need for high power economy requires the use of components having a non-linear amplitude transfer function and the spectrum at the output of such a component, for example a class C amplifier, will be wider than the spectrum at the input when the amplitude at the input varies. Therefore, in radio communication systems, preference is given to modulation methods which result in a modulated carrier signal of a substantially constant amplitude, which means the use of angle modulation. See, for example, the article "Tamed Frequency Modulation, a novel method to achieve spectrum economy in digital transmission" by F. de Jager, C. B. Dekker, in IEEE Transactions on Communications, vol. COM-26, No. 5, May 1978, pages 534-542.